This invention relates to method and apparatus for cooling of the electronics of a variable frequency drive associated with a refrigerant compressor.
Compressors used in many refrigeration systems generally require close control over the compressor motor speed in order to maintain the system within desired limits under varying load conditions. The compressors are therefore equipped with variable frequency drives (VFD) that contain power electronic components in the form of insulated gate bipolar transistors that can overheat and thereafter require cooling. The generally accepted procedure to provide cooling to the power electronics is to mount the transistors upon a heat sink and carry the heat away from the sink by circulating coolant in or around the heat sink. The capability of the heat sink and cooling system are of primary consideration in determining the power capacity of the VFD.
The heat sink is usually in the form of a relatively large block of material having good heat transfer and thermal inertia characteristics. A flow passage is formed in the block and coolant is circulated through the passage which absorbs excess heat and carries it out of the system.
The use of water to cool the VFD heat sink has proven to be a satisfactory means of cooling the VFD transistors, however, water cooling is difficult to control and the heat sink temperature sometimes can move out of desired operating range. This, in turn, can produce overheating of the VFD electronics and adversely effect the operation of the refrigeration system. In addition, the water cooling circuit requires additional water handling components such as pumps, heat exchangers and the like needed to discharge heat from the transistors into the surrounding ambient. This type of cooling equipment is generally complex, costly and requires a good deal of space to install.